The present invention relates generally to plural-component spray systems. In particular, the present invention relates to pressure relief systems for reciprocating fluid proportioners having at least two pumps.
Fluid proportioners comprise dispensing systems that receive separate inert fluid components, mix the components in a predetermined ratio and then dispense the components as an activated compound. For example, fluid proportioners are used to dispense epoxies and polyurethanes that solidify after mixing of a resin component and an activating material, which are individually inert. However, after mixing an immediate chemical reaction begins taking place that results in the cross-linking, curing, and solidification of the mixture. Therefore, the two components are routed separately into the proportioner so that they can remain segregated as long as possible. A manifold receives each component after it is pumped separately and mixes the components so the mixture can be dispensed from a sprayer coupled to the manifold.
A typical fluid proportioner comprises a pair of positive displacement pumps that individually draw in fluid from separate fluid hoppers and pump pressurized fluids to the mix manifold. The pumps are driven in synchronicity by a common motor, typically an air motor or hydraulic motor, having a reciprocating drive shaft. Most two component epoxies and polyurethanes are not, however, comprised of a 1:1 ratio of the components. Typically a first major component is needed in a higher concentration than a second minor component. In such a case, displacement of one pump is required to be larger than the other. The components are routed from the pumps to the mix manifold for blending. Additionally, a fluid manifold is positioned between the pumps and the mix manifold to permit each fluid to be independently circulated by its pump without mixing, thus segregating the mixing and curing part of the spray process from the pumping and pressurization part.
Because the fluids are circulated under high pressure, it is also desirable to provide pressure relief valves throughout the proportioner system. In particular, if one of the fluid lines becomes plugged, or one of the hoppers runs out of fluid, the other functioning pump will take the full force of the drive motor, causing an overpressure condition. For example, if a 4:1 mix ratio proportioner is spraying at 4,000 psi (˜27.6 MPa) and the major component pump runs out of fluid, the minor component pump will develop four times the normal operating pressure, or 16,000 psi (˜110.3 MPa). Excess pressures need to be vented to prevent failure of parts and unsafe conditions.
Typical proportioners include rupture disks that are permanently sealed, but open by tearing or bursting when overpressure conditions occur. Rupture disks can only be used one time and are used as secondary or back-up systems. Once the rupture disk breaks, the proportioner must be taken out of action until the disk can be replaced. Additionally, over pressure relief valves are used as the primary relief system. Relief valves are spring loaded and are set to open at a specific overpressure. The relief valves drain back to the hoppers or drain cans through drain lines. Ideally, the relief valves are not frequently used. As such, the relief valves and lines have a tendency to become plugged by the accumulation of dried and crystallized fluid from the previous use. This causes the relief valves to open at a much higher pressure or, in extreme cases, to not open at all. As such, there is a need to provide proportioners with more reliable and reusable relief valve systems.